The present invention relates to hydrodynamic bearings. In such bearings, a stationary bearing pad supports a rotating object such as a shaft via a pressurized fluid such as oil, air or water. Hydrodynamic bearings take advantage of the fact that when the rotating object moves, it does not slide along the top of the fluid. Instead, the fluid in contact with the rotating object adheres to the rotating object. Motion is thus accompanied by slip or shear between the fluid particles through the entire height of the fluid film. Thus, if the rotating object and the contacting layer of fluid move at a velocity that is known, the velocity at intermediate heights of the fluid thickness decreases at a known rate until the fluid in contact with the stationary bearing pad adheres to the bearing pad and is motionless. When, the bearing pad deflects at a small angle to the rotating because of the load resulting from its support of the rotating object, the fluid will be drawn into the wedge-shaped opening. Sufficient pressure is then generated in the fluid film to support the load. This fact is used in both thrust bearings and hydrodynamic journal bearings.
Thrust bearings and radial or journal bearings typically include shaft supporting pads spaced about an axis. The pads are spaced about an axis that generally corresponds to the longitudinal axis of the shaft to be supported for both thrust and journal bearings. This axis may be termed the major axis.
U.S. Pat. No. 3,107,955 to Trumpler discloses one example of a bearing having beam mounted bearing pads. The pads move with a pivoting or swing-type motion about a center located in front of the pad surface. This bearing, like many prior art bearings, is based only on a two dimensional model of pad deflection. Consequently, optimum wedge formation is not achieved.
In the Hall patent, U.S. Pat. No. 2,137,487, there is shown a hydrodynamic moveable pad bearing that develops its hydrodynamic wedge by sliding of its pad along spherical surfaces. Often the pad sticks and the corresponding wedge cannot be developed. In the Greene Patent, U.S. Pat. No. 3,930,691, elastomers provide the rocking. Such elastomers are subject to contamination and deterioration.
U.S. Pat. No. 4,099,799 to Etsion shows a non-unitary cantilever mounted resilient pad gas bearing. The disclosed bearing employs a pad mounted on a rectangular cantilever beam to produce a lubricating wedge between the pad face and the rotating shaft. Both thrust bearings and radial or journal bearings are shown.
U.S. Pat. No. 4,496,251 shows a pad that deflects with web-like ligaments to form a wedge shaped film of lubricant between the relatively moving parts.
U.S. Pat. No. 4,515,486 shows hydrodynamic thrust and journal bearings comprising several bearing pads, each having a face member and a support member that are separated and bonded together by an elastomeric material.
U.S. Pat. No. 4,526,482 shows hydrodynamic bearings primarily intended for process lubricated applications, i.e., the bearing is designed to work in a fluid. The hydrodynamic bearings are formed with a central section of the load carrying surface that is more compliant than the remainder of the bearings. Accordingly, the central section will deflect under load and form a pressure pocket of fluid to carry high loads.
It has also been noted, in Ide U.S. Pat. No. 4,676,668, that bearing pads may be spaced from the support member by at least one leg that provides flexibility in three directions. To provide flexibility in the plane of motion, the legs are angled inward to form a conical shape with the apex of the cone or point of intersection in front of the pad surface. Each leg has a section modulus that is relatively small in the direction of desired motion to permit compensation for misalignments. These teachings are applicable to both journal and thrust bearings.
Presently, the most widely used hydrodynamic thrust bearing is the so-called Kingsbury shoe-type bearing. The shoe-type Kingsbury bearing is characterized by a complex structure that includes pivoted shoes, a thrust collar which rotates with the shaft and applies load to the shoes, a base ring for supporting the shoes, a housing or mounting which contains and supports the internal bearing elements, a lubricating system and a cooling system. Because of this complex structure, Kingsbury shoe-type bearings are typically extraordinarily expensive.
Additional background relating to hydrodynamic bearings may be gleaned by reviewing recently issued patents including U.S. Pat. No. 5,255,984 that shows a variable characteristic thrust bearing. The bearing includes separately formed pads of various forms and materials supported in a carrier. The carrier is constructed such that the pads may be located in separate openings to vary the support characteristics.
U.S. Pat. No. 5,222,815 shows a variety of unitary bearings, including journal, thrust and combined radial and thrust bearings of the type having beam mounted bearing pads. The pads and support structure may be integrally formed as a single piece. Similarly, U.S. Pat. No. 5,137,373 shows thrust, radial and combined radial/thrust bearings in which the pads and support structure are integrally formed as a single piece.
U.S. Pat. No. 5,125,754 shows thrust and journal bearings having a modular construction. In general, the bearings shown therein include separate pads or pad portions mounted in a separate carrier. Various pad and carrier configurations are disclosed.
U.S. Pat. No. 5,102,236 shows hydrodynamic thrust and radial bearings having a continuous beam mounted shaft support surface.
This application is specifically directed to the problem of hot oil carryover in hydrodynamic bearings. As recognized by persons skilled in the art, hot oil carryover, i.e., lubricant flow from one pad's trailing edge to the leading edge of the subsequent pad, can lead to reduced performance and even failure of pad type bearings.
U.S. Pat. No. 4,348,065 to Yoshioka addresses the problem of hot oil carryover. Yoshioka shows a thrust bearing or tapered land bearing which includes lubricant feeding nozzle holes. The nozzle holes are disposed near the leading edge of a tapered surface of a thrust bearing surface. This arrangement is said to minimize hot oil carryover.